JP7295947B2 - Porous metal foil or wire, and capacitor anode made therefrom, and method of making same - Google Patents

Description

This application is made under 35 U.S.C. It claims the benefits of calligraphy.

The present invention relates to metal foils and wires, and anodes and capacitors containing same. In particular, the present invention relates to porous metal foils or wires, including tantalum foils.

The invention further relates to methods of manufacturing porous metal foils or wires, as well as methods of manufacturing anodes and capacitors containing porous metal foils.

Valve metal powders, such as tantalum powders, are commonly used in the manufacture of capacitor electrodes, among other uses.

Currently, tantalum powder, for example, is generally manufactured via one of two methods: a mechanical process or a chemical process. Mechanical processes include ingot formation by electron beam melting of tantalum, ingot hydrogenation, hydride milling, and subsequent dehydrogenation, crushing, and heat treatment steps. This process generally produces high purity powders.

Another commonly used process for the production of tantalum powder is a chemical process. Several chemical methods for tantalum powder production are known in the art. U.S. Pat. No. 4,067,736 issued to Vartanian and U.S. Pat. No. 4,149,876 issued to Rerat describe a chemical preparation involving sodium reduction of potassium fluorotantalate ( _{K2TaF7 )} . Regarding the process. A review of typical techniques can be found in Bergman et al. See also the background section of US Pat. No. 4,684,399 issued to No. 4,684,399 and US Pat. All patents and publications are hereby incorporated by reference in their entirety.

Tantalum powders produced by chemical methods are well suited for use in capacitors, for example, because they generally have higher surface areas than powders produced by mechanical methods. Chemical methods generally involve chemical reduction of tantalum compounds with reducing agents. Typical reducing agents include hydrogen and active metals such as sodium, potassium, magnesium, and calcium. Exemplary _tantalum compounds include, but are not limited to, potassium _{fluorotantalate} ( _K2TaF7 ), sodium fluorotantalate ( _Na2TaF7 ), tantalum pentachloride ( _TaCl5 ), tantalum pentafluoride (TaF ₅ ), and mixtures thereof. The most widely used chemical process is the reduction of _{K2TaF7 with} liquid sodium.

In the chemical reduction of valve metal powders such as tantalum powder, potassium fluorotantalate is recovered, melted and reduced by sodium reduction to tantalum metal powder. The dried tantalum powder may then be recovered, optionally thermally agglomerated under vacuum to avoid oxidation of the tantalum, and milled. Since the oxygen concentration of the valve metal material can be important in the manufacture of capacitors, this granular powder is then typically made of an alkaline earth metal (e.g. magnesium) that has a higher affinity for oxygen than the valve metal. It is deoxidized at high temperatures (eg, up to about 1000° C. or higher) in the presence of a getter material such as. Under standard atmospheric conditions (e.g., approximately 760 mm Hg) for post-deoxygenation processes to dissolve metal and refractory oxide contaminants (e.g., magnesium and magnesium oxide contaminants) before the material is further processed. The acid leaching that takes place can be done with a mineral acid solution that includes, for example, sulfuric acid and nitric acid. The acid-leached powder can be washed and dried, followed by compaction, sintering, and anodization in conventional manner to produce sintered porous bodies, such as anodes for capacitors.

Most of the efforts in tantalum powder development have been driven by the capacitor anode industry, where powders have been manufactured for this specific purpose only.

As technology advances and electrical devices become smaller and smaller, there is a need to provide anodes that can be used in such small or miniaturized devices. Many of today's anodes, as indicated above, use tantalum powder, the powder is pressed into the anode shape, the anode is sintered to form a sintered body, which is then used as the electrolyte. It is manufactured by anodizing inside to form a dielectric oxide film on the sintered body and finally forming a capacitor anode. The pressing and sintering method, which uses tantalum powder as a starting material, presents a problem because it can only produce very small anodes. Therefore, it is generally understood that it is extremely difficult to obtain acceptable anodes thinner than 0.2 mm by using conventional pressing and sintering methods.

Therefore, there is a need in the industry to provide acceptable anodes that can be consistently thin so that anodes less than 0.2 mm thick can be formed.

A feature of the present invention is to provide a porous metal foil or wire that can be used to form a thin capacitor anode.

Another feature of the invention is to provide anodes and capacitors fabricated from porous metal foils or wires.

A further feature of the invention is to provide a method for forming a porous metal foil or wire that can be used in the manufacture of anodes.

Additional features and advantages of the invention will be set forth in part in the description that follows, and in part will be apparent from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by means of the elements and combinations particularly pointed out in the description and appended claims.

To achieve these and other advantages, and in accordance with the objectives of the invention, and as embodied and broadly described herein, the present invention is directed, in part, to porous metal foils or wires. A porous metal foil or wire has a thickness and an outer surface. The porous metal foil or porous metal wire comprises, includes, or is a tantalum foil having a nominal thickness of 0.2 mm or less, or from about 0.05 mm to about 1.0 mm. has a diameter of The porous metal foil or porous metal wire further has porosity on at least the outer surface of the metal foil or metal wire.

The present invention further relates to capacitor anodes comprising or formed from the porous metal foils of the present invention and dielectric oxide films formed on the porous metal foils.

The present invention also relates to a method of forming a porous foil or wire of the present invention comprising exposing a metal foil or wire comprising or being tantalum to an oxidation treatment that forms an oxide layer on the metal foil or wire. related. Subsequently, the method further includes exposing the metal foil or wire to a deoxidizing treatment such that porosity is formed on at least the surface of the metal foil or wire.

It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are intended to provide further explanation of the invention as claimed.

FIG. 1 is an SEM photograph of foils and wires formed according to the invention, showing the presence of a porous structure. In particular, as shown in the SEM photographs, the etched surface resembles a fine-grained exposed surface. FIG. 2 is a flowchart illustrating one example of a process that can be used with the present invention.

The present invention relates to porous metal foils or porous metal wires. Further, the present invention relates to capacitor anodes comprising or formed from porous metal foils and/or porous metal wires. Additionally, the present invention relates to methods of forming the porous metal foils or wires of the present invention. The invention also relates to other aspects described herein.

More specifically, the porous metal foil or wire of the present invention has a thickness and an outer surface (ie, an outer surface or exposed surface). The porous metal foil comprises, comprises, consists essentially of, consists of, or is a tantalum foil having a nominal thickness. This thickness may be, for example, 0.2 mm or less. Furthermore, the porous metal foil has porosity at least on the outer surface.

As noted with respect to metal foil thickness or tantalum foil thickness, this thickness may be 0.2 mm or less, or other thicknesses. For example, the thickness is 0.01 mm to 0.2 mm, or 0.02 mm to 0.2 mm, or 0.012 mm to 0.2 mm, or 0.025 mm to 0.15 mm, or 0.05 mm to 0.1 mm, or 0.04 mm to 0.1 mm, or 0.015 mm to 0.09 mm, and other thicknesses within or outside these ranges.

For purposes of the present invention, metal foil may be considered a metal ribbon or metal strip having the thicknesses described herein. For purposes of the present invention, tantalum foil may be considered a tantalum ribbon or strip having the thicknesses described herein. The metal foil, such as tantalum foil, may be of powder metallurgy grade or ingot derived grade (eg, electron beam (EB) grade). Metal foils such as tantalum foil (or starting metal foils such as starting tantalum foil) are available from Global Advanced Metals USA, Alfa Aesar, and H.I. C. It is commercially available from several suppliers including Starck.

The porous metal foils of the present invention may have a metal purity that may be at least 99.9% Ta (by weight) (excluding gases). The purity may be, for example, at least 99.95% Ta, or at least 99.99% Ta, or such as from about 99.9% Ta to 99.995% Ta or more.

Optionally, the porous metal foil may have a carbon content or amount of less than 200 ppm, for example less than 100 ppm, or less than 50 ppm, or less than 25 ppm. For example, the amount or content of carbon in the porous metal foil is from about 5 ppm to about 199 ppm, or from about 10 ppm to 175 ppm, or from about 15 ppm to 150 ppm, or from about 25 ppm to 150 ppm of carbon (elemental form). ).

The porous metal foil may have the purity levels described above for tantalum in combination with any one of these carbon content or carbon amount ranges.

The porous metal foils of the present invention also have the porosity indicated herein. This porosity is present at least on the outer surface. The porosity on the outer surface may be uniform or non-uniform. Porosity may be understood as a plurality of pores and/or depressions.

The porosity of the metal foil may be present not only on the outer surface or on the outer surface, but optionally also below the surface (eg, within the foil or within the foil). This porosity, if present below the outer surface (e.g., within the thickness of the porous metal foil), may be through the entire thickness, or through certain regions or portions of the thickness. . The porosity of the lower portion of the outer surface may be uniform or non-uniform. The depth of any porosity below the outer surface may or may not be uniform with respect to the position of the porosity from the outer surface. In other words, for example, porosity may be present at a depth of five microns (5 micrometers) from the outer surface of one portion of the metal foil, but at the same depth of five microns (5 micrometers) on another portion. should not exist.

In the present invention, due to the porosity that is formed, the exposed surface has "islands" of solid metal that appear as primary particles or agglomerates. The exposed surface and grainy appearance can be considered an etched particulate exposed surface, or an etched exposed surface that appears as particulates or agglomerated particulates. These etched particulate exposed surfaces can have sizes that can be quantified or measured, such as primary particle size.

Thus, the metal foil or wire has a thickness of about 5 nm to about 500 nm, such as about 5 nm to about 400 nm, about 5 nm to about 300 nm, about 5 nm to about 200 nm, about 10 nm to about 500 nm, about 20 nm to about 500 nm, about 50 nm to about 500 nm. , about 50 nm to about 400 nm, about 50 nm to about 300 nm, about 50 nm to about 200 nm, or other ranges within or outside these ranges (exposed surface as shown in FIG. 1). at ). Each of these ranges provided herein may be the average grain size relative to the particulate surface present on the exposed surface of the foil or wire.

In the present invention, from the formation of porosity on at least one exposed surface or on more than one exposed surface, generally two exposed surfaces (top and bottom surfaces of the foil, not the edges), or the surface area of all faces is at least 25%, at least 50%, at least 75%, at least 100%, at least 125%, or at least 150% increase (such as about a 25% to 150% increase in exposed surface area). The increase in surface area may be a BET (m ² /g) measurement that measures total surface area or other external surface area measurements.

The porous metal foil of the present invention has a porosity of from about 1% to about 100% by volume, from about 5% to about 75% by volume, from about 5% to about 50% by volume, based on the total volume of the metal foil. 100% by volume or less, 75% by volume or less, 50% by volume or less, 30% by volume or less, 20% by volume, such as %, about 5% to about 30% by volume, about 2% to about 20% by volume, and like amounts % or less, with porosity present. As noted, for any porosity present in this volume percent, the porosity may be uniform or non-uniform when present in the porous metal foil.

Generally, the porosity of the outer surface, if present, is present in a greater amount (eg, number of pores and/or density of porosity) than any porosity below or below the outer surface. For example, the porosity on the outer surface may be the same amount, or may be at least 10% more porosity than any region below the outer surface. For example, the porosity is at least 20% more, at least 50% more, at least 75% more, in terms of the number of pores present in the outer surface compared to either the area below the outer surface or within the metal foil. % more, at least 100% more, at least 150% more, at least 200% more. The porosity from the surface to the interior may be graded, where the degree and/or uniformity of porosity decreases from the exterior to the interior.

As another option, the porosity below the outer surface or within the metal foil may be at a level of at least five microns (5 micrometers) below the outer surface, if desired. For example, the level at which porosity exists is at least ten microns (10 micrometers) below the outer surface, at least twenty-five microns (25 micrometers) below the outer surface, at least fifty microns (50 micrometers) below the outer surface, or It may be at least one hundred microns (100 micrometers) below, or some other amount of depth. Any porosity under the outer surface may be uniform or non-uniform, and/or uniformly present at a certain depth or uniform at a certain depth. does not have to exist. For example, just by way of example, porosity may be present in one region of a porous metal foil at a particular depth, but not in another region at the same depth. This is one example of when non-uniform porosity exists, especially below the surface. In another example, the density of porosity in one region at a particular depth can be the same or different compared to another region at the same depth.

The porous metal foils of the present invention may have any length, any width, and, as noted, may have a nominal thickness generally no greater than 0.2 mm. For example, the length of the metal foil can be from about 10 mm to about 50 mm, or other lengths within or outside these upper or lower limits. The porous metal foil may have a width of about 5 mm to about 25 mm, or other widths within or outside these upper or lower limits.

A porous metal wire having a diameter and an outer surface comprises, comprises, consists essentially of, consists of, or is a tantalum wire having porosity. This starting metal wire, such as the starting tantalum wire for making the wire of the present invention, is commercially available from the same suppliers as the metal foils described herein. With respect to the porous metal wire, the porous metal wire of the present invention has the same features and characteristics with respect to porosity as described herein for the porous metal foil. The discussion herein of porosity features, characteristics, and properties for metal foils applies equally to this porous metal wire embodiment. The discussion of tantalum and its purity with respect to the porous metal foil applies equally herein to the porous metal wire embodiment, each of which is incorporated into this wire embodiment to avoid repetition. be.

The porous metal wires of the present invention, as described, have an outer surface and have a diameter that can be from about 0.05 mm to about 1.0 mm. The diameter may be from about 0.05 mm to about 0.75 mm, or from about 0.05 mm to about 0.5 mm, or other diameters within or outside any one of these ranges. The porous metal wire can be of any length. The term "diameter" generally refers to a circular cross-sectional shape, but when the cross-sectional shape is square or other such geometric shape, the term diameter also includes these other shapes. However, diameter is then understood to represent the cross-sectional length and/or width parameters for these other shapes.

The porous metal foils of the present invention can be utilized in, or formed into, capacitor anodes. The capacitor anode comprises, comprises, consists essentially of, consists of, or is the porous metal foil of the present invention. The capacitor anode further includes a dielectric oxide film or layer present or formed on the porous metal foil. The porous metal foil forming the capacitor anode may be a sintered porous metal foil.

Furthermore, the invention relates to a capacitor comprising the capacitor anode of the invention.

The capacitor anode of the present invention may comprise the porous metal wire of the present invention, which can be used for the capacitor anode and/or capacitor of the present invention.

The present invention further relates to methods of forming the porous metal foils and/or porous metal wires of the present invention.

A method of forming a porous metal foil or wire of the present invention may include exposing the metal foil or wire to an oxidation treatment that forms an oxide layer on at least a surface of the metal foil or wire. may comprise exposing to, may consist essentially of exposing to the oxidizing treatment, or may consist of exposing to the oxidizing treatment. The method further includes exposing the metal foil or wire to a deoxidizing treatment such that porosity is formed on at least the surface of the metal foil or wire after the oxidation treatment. As indicated, the porosity may be formed on at least one outer surface, on some outer surfaces, or on all outer surfaces, and optionally one below the surface as described above. or may include multiple interior regions or depth portions. FIG. 2 shows a schematic of these steps.

In the method of the invention, the step of exposing the metal foil or wire to an oxidation treatment may be repeated one or more times. For example, the oxidation treatment step may be repeated once, twice, three times, or from 1 to 10 times or more. The conditions for each step, if repeated, may be the same or different for other oxidation treatment steps.

The deoxygenation treatment step may be repeated one or more times. For example, this step may be repeated at least once, or at least two times, or at least three times, or from 1 to 10 or more times. The conditions for each deoxygenation step (if repeated) may be the same as for the preceding deoxygenation step or different.

Optionally, the oxidation treatment step and the deoxygenation treatment step may each be repeated one or more times.

With respect to the oxidation treatment, this step may comprise calcining the metal foil or wire in air at a temperature that causes oxidation of the metal foil or wire, essentially may consist of, may consist of calcining thereof, or may be calcining thereof. For example, the temperature may be at least 500°C. The oxidation treatment may be for at least 5 minutes or longer, such as 5 minutes to 10 hours or longer. One example of an oxidation treatment is therefore calcination of a metal foil or wire at a temperature of at least 500° C. for at least 5 minutes in air. For example, calcination in air can be at a temperature of about 500° C. to about 650° C. for a time of about 5 minutes to about 10 hours or more.

The oxidation treatment may be, comprises, comprises, consists essentially of, or consists of a chemical oxidation treatment. An example of a chemical oxidation treatment is treatment using acids such as HF acid, eg at elevated temperatures (eg at temperatures between 40° C. and 600° C.). The chemical oxidation treatment may be treatment using an alkaline bath at elevated temperatures (eg, at temperatures between 40° C. and 600° C.).

Regarding the oxidation treatment that forms an oxide layer on the metal foil or wire, the oxidation treatment is at least 1 micron (1 micrometer) thick, or at least 5 microns (5 micrometers) thick, or at least 10 microns ( 10 micrometers), or at least fifty microns (50 micrometers) and similar thicknesses.

Optionally, the oxidation treatment reduces oxidation of the foil or wire to 50% or less, 40% or less, 30% or less, 20% or less, 10% or less with respect to the total volume of the metal foil or metal wire. can cause it.

With respect to the deoxygenation treatment, this step may include contacting a metal foil or wire (that has been subjected to an oxidation treatment) to an oxygen getter material at an elevated temperature. It may consist essentially of, consist of, or be the process. For example, this temperature may be at least 500°C. The length of time the metal foil or wire is in contact with the oxygen getter material may be at least 5 minutes. For example, just by way of example, the deoxidizing treatment may comprise contacting a metal foil or wire with an oxygen getter material at a temperature of at least about 500° C. for a time period of from about 5 minutes to about 10 hours or more. , or the process thereof. For example, the temperature can be from about 600°C to 1300°C, or from about 700°C to 1300°C, or from about 700°C to about 1200°C, or from about 700°C to about 1000°C.

Optionally, after the deoxidation step, the metal foil or wire may then be subjected to sintering, such as vacuum sintering, as desired. The sintering temperature may be from about 1000°C to about 1600°C. The length of time for sintering may be from about 5 minutes to about 10 hours.

Optionally, the metal foil or wire after deoxidation treatment may be subjected to acid leaching (eg HNO3), then rinsed, and then dried.

Optionally, the oxidation and deoxygenation treatments may be done without any annealing between the oxidation and deoxygenation treatments.

Optionally, the metal foil may be anodized in an electrolyte to form a dielectric oxide film or layer on the metal foil to form the capacitor anode of the present invention.

A capacitor anode of the present invention may have a leakage current of 10 nA/uFV or less. This leakage current is, for example, 5 nA/uFV or less, or 1 nA/uFV or less, about 0.1 nA/uFV to about 10 nA/uFV, or about 0.1 nA/uFV to about 5 nA/uFV, or about 0.1 nA/uFV. to about 1 nA/uFV.

The invention will be further clarified by the following examples, which are intended to be illustrative of the invention.

Example 1
In this example, porous metal foils and wires were produced according to the present invention.

A commercial starting 0.07 mm thick tantalum foil manufactured by Global Advanced Metals, KK was used. The foil was cut to dimensions such that each foil strip was 10 mm wide and 50 mm long. The tantalum foil was then acid leached with 30% _HNO3 , rinsed with deionized water, and then dried.

Additionally, a starting tantalum wire with a diameter of 0.5 mm was cut to a length of 350 mm, wound into a spring shape, then rinsed with acetone and dried. This starting capacitor grade tantalum wire was manufactured by Global Advanced Metals, USA.

Multiple pieces of tantalum foil were used in the experiment, and multiple pieces of wire of a certain diameter were used in the experiment. A portion of the tantalum foil and a portion of the tantalum wire were pre-subjected to chemical oxidation in a molten KOH bath at approximately 500° C. for 5 minutes, rinsed with deionized water and dried. This process is denoted by "DGS" in the table.

All samples were then placed in ceramic bowls and subjected to one of the following treatments:
a) 550° C. for 30 minutes b) 600° C. for 30 minutes c) 550° C. for 120 minutes d) 570° C. for 120 minutes or e) no calcination in air.

In addition, a portion of the sample was then optionally vacuum annealed at 1400° C. for 20 minutes.

All samples were then subjected to deoxygenation treatment including using magnesium chips. Specifically, 8 grams of magnesium chips were placed in the bottom of a tantalum box measuring 100 mm long, 60 mm wide and 25 mm high, samples of tantalum foil and tantalum wire were placed on top of the magnesium chips and the lid was closed. , to either 750° C. or 980° C. for a total of approximately 5 hours. Part of this time involved an argon atmosphere. After cooling, air inertization was performed by repeating the cycle of vacuum pumping and air introduction.

The deoxidized material was then acid leached using HNO ₃ (60% concentration). The material was then rinsed with deionized water and dried. This deoxygenation treatment was repeated twice using the same conditions.

For anode formation, a 0.5 mm diameter wire with a length of 60 mm was welded to the sample and the tantalum foil and wire were subjected to vacuum sintering at 1200° C. for 20 minutes.

For anode formation, formation at 20 volts with 0.1 vol.% H ₃ PO ₄ was used at 60° C. for 120 minutes and the current density for the target Vf was 20 μA/mm ² . After that, the electrical properties were measured.

Electrical measurements in liquid electrolytes were performed at 25° C. with a bias voltage of 120 Hz and 1.5 volts in 30 vol % H ₂ SO ₄ for capacitance and 10 vol % for DC leakage current H ₃ PO ₄ at 25° C. with three charges at 14 volts.

The results of the experiments are shown in the table below.

By visual observation, and considering the electrical properties shown above, a porous structure was formed directly on at least the surfaces of the foil and wire by using the oxidation and deoxidation treatment of the present invention. These examples yielded thin anode materials less than 0.1 mm thick, which have sufficient capacitance and DC leakage current characteristics for commercial utility, especially for use in small devices. rice field.

The present invention includes the following aspects/embodiments/features in any order and/or in any combination.
1. A porous metal foil or wire having a thickness and an outer surface, said porous metal foil or wire a) having a nominal thickness of 0.2 mm or less or a diameter of about 0.05 mm to about 1.0 mm tantalum foil; and b) a porous metal foil or wire with porosity on at least said outer surface.
2. A porous metal foil or wire according to any of the above or the following embodiments/features/aspects, wherein said nominal thickness is between 0.01 mm and 0.2 mm.
3. A porous metal foil or wire according to any of the above or the following embodiments/features/aspects, wherein said diameter is between 0.05 mm and 0.5 mm.
4. A porous metal foil or wire according to any of the above or the following embodiments/features/aspects, wherein said nominal thickness is between 0.02 mm and 0.18 mm.
5. A porous metal foil or wire according to any of the above or the following embodiments/features/aspects, wherein said nominal thickness is between 0.03 mm and 0.18 mm.
6. A porous metal foil or wire according to any of the preceding or following embodiments/features/aspects, wherein said porous metal foil or wire has a purity level of at least 99.9% Ta.
7. A porous metal foil according to any preceding or following embodiment/feature/aspect, wherein said porous metal foil or wire has a purity level of at least 99.9% Ta and a carbon content of less than 200 ppm or wire.
8. A porous metal foil according to any preceding or following embodiment/feature/aspect, wherein said porous metal foil or wire has a purity level of at least 99.9% Ta and a carbon content of less than 100 ppm or wire.
9. The porous metal foil or wire of any preceding or following embodiment/feature/aspect, wherein the porous metal foil or wire has a purity level of at least 99.9% Ta and a carbon content of about 5 ppm to about 100 ppm. metal foil or wire.
10. A porous metal foil or wire according to any of the preceding or following embodiments/features/aspects, wherein the etched particulate exposed surface has an average particle size of from about 5 nm to about 500 nm.
11. A porous metal foil or wire according to any of the above or the following embodiments/features/aspects, wherein the etched particulate exposed surface has an average particle size of from about 50 nm to about 200 nm.
12. A porous metal foil or wire according to any of the above or following embodiments/features/aspects, wherein said porosity further resides at a level at least 5 microns below said outer surface.
13. A porous metal foil or wire according to any of the above or following embodiments/features/aspects, wherein said porosity further resides at a level at least 10 microns below said outer surface.
14. A porous metal foil or wire according to any of the above or following embodiments/features/aspects, wherein said porosity further resides at a level at least 50 microns below said outer surface.
15. Any preceding or following embodiment/feature/aspect, wherein the metal foil has a length of 10 mm to 50 mm, a width of 5 mm to 25 mm, and a nominal thickness of 0.01 mm to 0.2 mm. Porous metal foil or wire.
16. A capacitor anode comprising the porous metal foil of any of the above or any of the following embodiments/features/aspects and a dielectric oxide film on the porous metal foil.
17. A capacitor anode according to any of the above or the following embodiments/features/aspects, wherein the porous metal foil is a sintered porous metal foil.
18. A capacitor comprising a capacitor anode according to any of the embodiments/features/aspects above or below.
19. A method of forming a porous metal foil or wire according to any of the above or any of the following embodiments/features/aspects, the method comprising:
a. exposing a metal foil or wire to an oxidation treatment that forms an oxide layer on the metal foil or wire;
b. exposing the metal foil or wire of step a) to a deoxidizing treatment to form porosity on at least the surface of said metal foil or wire;
A method, including
20. The method of any preceding or following embodiment/feature/aspect, wherein said step b) is repeated one or more times after said step a).
21. The method of any preceding or following embodiment/feature/aspect, wherein step a) is repeated one or more times and step b) is repeated one or more times.
22. The method of any preceding or following embodiment/feature/aspect, wherein the oxidation treatment comprises calcining the metal foil or wire at a temperature of at least 500° C. for at least 5 minutes in air.
23. Any of the preceding or following embodiments/features/ A method according to an aspect.
24. The method of any preceding or following embodiment/feature/aspect, further comprising vacuum sintering the metal foil or wire after step b).
25. The method of any preceding or following embodiment/feature/aspect, wherein said oxidation treatment comprises a chemical oxidation treatment.
26. Embodiments of any of the above or the following, wherein said deoxidizing treatment comprises exposing said metal foil or wire of step a) to an oxygen getter material at a temperature of at least 500° C. for at least 5 minutes/ A method according to an aspect/aspect.
27. wherein the deoxidizing treatment comprises exposing the metal foil or wire of step a) to an oxygen getter material at a temperature of about 700° C. to about 1300° C. for a time of about 5 minutes to about 10 hours. or any of the following embodiments/features/aspects.
28. Any preceding or following embodiment/feature/aspect according to any preceding or following embodiment/feature/aspect, further comprising, after step b), subjecting the metal foil or wire to an acid leaching followed by a water rinse followed by drying. Method.
29. after step b), sintering the metal foil, and then anodizing the metal foil in an electrolyte to form a dielectric oxide film on the metal foil to form a capacitor anode. or any of the following embodiments/features/aspects.
30. The method of any preceding or following embodiment/feature/aspect, wherein said oxidation treatment forms said oxide layer having a thickness of at least 5 microns.
31. The method of any preceding or following embodiment/feature/aspect, wherein said oxidation treatment forms said oxide layer having a thickness of at least 10 microns.
32. The method of any preceding or following embodiment/feature/aspect, wherein said oxidation treatment forms said oxide layer having a thickness of at least 50 microns.
33. A capacitor anode according to any preceding or following embodiment/feature/aspect, wherein said capacitor anode has a leakage current of 10 nA/uFV or less.
34. A capacitor anode according to any preceding or following embodiment/feature/aspect, wherein said capacitor anode has a leakage current between 0.1 nA/uFV and 1.0 nA/uFV.
35. The method of any preceding or following embodiment/feature/aspect, wherein said oxidation treatment and said deoxygenation treatment are performed without annealing therebetween.

The invention can include any combination of these various features or embodiments described above and/or below as indicated in the sentences and/or paragraphs. Any combination of features disclosed herein is considered part of the invention and is not intended to be limiting as to features that can be combined.

Applicants specifically incorporate the entire contents of all cited references in this disclosure. Further, when an amount, concentration, or other value or parameter is given as either a range, a preferred range, or a list of upper preferred and lower preferred values, this indicates whether the ranges are separately disclosed. Regardless, it is to be understood as specifically disclosing all ranges that may be formed from any pair of any upper or preferred value and any lower or preferred value. When a numerical range is stated herein, unless otherwise specified, the range is intended to include the endpoints and all integers and fractions within the range. It is not intended that the scope of the invention be limited to the specific values set forth in defining the range.

Other embodiments of the invention will be apparent to those skilled in the art from consideration of the specification and practice of the invention disclosed herein. It is intended that the specification and examples be considered as exemplary only, with a true scope and spirit of the invention being indicated by the following claims and their equivalents.

Claims (27)

A porous metal foil or wire having a thickness and an outer surface, said porous metal foil or wire comprising: a) a tantalum foil having a nominal thickness of 0.2 mm or less or a diameter of 0.05 mm to 1.0 mm; and b) porosity in at least said outer surface, said porosity further present at a level at least 50 microns below said outer surface, said porous metal foil or wire having a purity level of at least 99.9% Ta. wherein said porous metal foil or wire has a carbon content of less than 200 ppm . The porous metal foil or wire of claim 1, wherein said nominal thickness is between 0.01 mm and 0.2 mm. A porous metal foil or wire according to claim 1, wherein said diameter is between 0.05 mm and 0.5 mm. The porous metal foil or wire of claim 1, wherein said nominal thickness is between 0.02 mm and 0.18 mm. The porous metal foil or wire of claim 1, wherein said nominal thickness is between 0.03 mm and 0.18 mm. 2. The porous metal foil or wire of claim 1, wherein the porous metal foil or wire has a carbon content of less than 100 ppm. The porous metal foil or wire according to claim 1, wherein said porous metal foil or wire has a carbon content of 5 ppm to 100 ppm. 2. The porous metal foil or wire of claim 1, wherein the outer surface comprises pores and an exposed particulate surface, the particulate surface having an average primary particle size of 5 nm to 500 nm. 2. The porous metal foil or wire of claim 1, wherein the outer surface comprises pores and an exposed particulate surface, the particulate surface having an average primary particle size of 50 nm to 200 nm. The porous metal foil or wire of claim 1, wherein the metal foil has a length of 10mm to 50mm, a width of 5mm to 25mm, and a nominal thickness of 0.01mm to 0.2mm. A capacitor anode comprising the porous metal foil according to any one of claims 1 to 10 and a dielectric oxide film on the porous metal foil. 12. The capacitor anode of claim 11 , wherein said porous metal foil is a sintered porous metal foil. A capacitor comprising a capacitor anode according to claim 11 or 12 . A method of forming a porous metal foil or wire according to claim 1, the method comprising:
a. exposing a metal foil or wire to an oxidation treatment that forms an oxide layer on the metal foil or wire;
b. exposing the metal foil or wire of step a) to a deoxidizing treatment to form porosity on at least the surface of said metal foil or wire;
wherein said oxidation treatment forms said oxide layer having a thickness of at least 50 microns. 15. The method of claim 14 , wherein step b) is repeated one or more times after step a). 15. The method of claim 14 , wherein step a) is repeated one or more times and step b) is repeated one or more times. 15. The method of claim 14 , wherein said oxidation treatment comprises calcination of said metal foil or wire at a temperature of at least 500<0>C in air for at least 5 minutes. 15. The method of claim 14 , wherein said oxidation treatment comprises calcination of said metal foil or wire at a temperature of 500-650° C. in air for a period of 5 minutes-10 hours. 15. The method of claim 14 , further comprising vacuum sintering the metal foil or wire after step b). 15. The method of claim 14 , wherein said oxidation treatment comprises a chemical oxidation treatment. 15. The method of claim 14 , wherein said deoxidizing treatment comprises exposing said metal foil or wire of step a) to an oxygen getter material at a temperature of at least 500<0>C for at least 5 minutes. 15. The method of claim 14 , wherein the deoxidizing treatment comprises exposing the metal foil or wire of step a) to an oxygen getter material at a temperature of 700° C. to 1300° C. for a period of 5 minutes to 10 hours. the method of. 15. The method of claim 14 , further comprising subjecting the metal foil or wire to acid leaching, followed by rinsing with water, and then drying after step b). After step b), further comprising sintering the metal foil and then anodizing the metal foil in an electrolyte to form a dielectric oxide film on the metal foil to form a capacitor anode. 15. The method of claim 14 . 13. A capacitor anode according to claim 11 or 12 , wherein said capacitor anode has a leakage current of 10 nA/uFV or less. A capacitor anode according to claim 11 or 12 , wherein said capacitor anode has a leakage current of 0.1 nA/uFV to 1.0 nA/uFV. A method according to any one of claims 14 to 24 , wherein said oxidation treatment and said deoxygenation treatment are done without annealing therebetween.

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